Rep. Lou Barletta, R-Pa., officially announced his bid to unseat Casey, a two-term senator, on Tuesday. In a campaign video, he referenced making "Pennsylvania and America great again" and said that "Pennsylvania deserves better than an obstructionist senator."
Casey is one of several Democrats facing re-election next year in a state that Trump won in 2016, though by only a narrow margin in Pennsylvania's case. Party incumbents in Ohio, West Virginia, Missouri, North Dakota, Indiana and Michigan also will have to fight for seats next year.
The Republican Party currently controls the Senate with 52 seats and has opportunities to add more with a favorable map in 2018. However, Democrats see a chance to perform better than expected as Trump faces a dismal approval rating.
Barletta, 61, has served in the House since 2011. A congressman who takes a hard line on illegal immigration, Barletta supported Trump early in his presidential run. Trump had urged him to run for Senate.
Barletta previously was mayor of the eastern Pennsylvania city of Hazleton. His largely rural 11th congressional district in the central-eastern part of the state contains Hazleton.
Casey, 57, won his last re-election bid in 2012 by about 9 percentage points.
Casey's counterpart, Sen. Pat Toomey, R-Pa., won his re-election bid by 1.5 percentage points last year. Trump won the state by less than a percentage point.
In a statement, Pennsylvania Democratic Party spokesman Max Steele called Barletta an "ethically challenged congressman" and said "the commonwealth deserves better" than him. He highlighted Barletta's vote for the American Health Care Act, the House GOP's Obamacare replacement that was expected to lead to millions more Americans uninsured and higher costs for older and poorer Americans.